Process for NGL recovery from pressurized liquid natural gas

Abstract

A process for removing hydrocarbons less volatile than methane from a pressurized liquid natural gas (PLNG). PLNG is heated in a heat exchanger, thereby vaporizing at least a portion of the PLNG. The partially vaporized PLNG is passed to a fractionation column. A liquid stream enriched with hydrocarbons (C2+ or C3+) less volatile than methane is withdrawn from a lower portion of the fractionation column and a vapor stream lean in the hydrocarbons less volatile than methane is withdrawn from an upper portion of the fractionation column. The withdrawn vapor stream is passed to the heat exchanger to condense the vapor to produce PLNG lean in hydrocarbons less volatile than methane.

What is claimed is:  
     
       1. A process for removing hydrocarbons less volatile than methane from a pressurized liquid natural gas (PLNG), comprising the steps of: 
       (a) heating the PLNG in a heat exchanger, thereby vaporizing at least a portion of the PLNG;  
       (b) passing the partially vaporized PLNG to a fractionation column;  
       (c) withdrawing a liquid stream enriched with hydrocarbons less volatile than methane from a lower portion of the fractionation column;  
       (d) withdrawing a vapor stream from an upper portion of the fractionation column; and  
       (e) passing the vapor stream to the heat exchanger to condense the vapor to produce PLNG lean in hydrocarbons less volatile than methane.  
     
     
       2. The process of  claim 1  further comprising, before step (a), the additional step of withdrawing a portion of PLNG and passing the withdrawn portion to the fractionation column to provide liquid reflux for the fractionation column. 
     
     
       3. The process of  claim 1  further comprising the additional step of heating the withdrawn liquid stream of step (c) and returning the vaporized portion of the heated withdrawn liquid stream to the fractionation column for reboiler duty. 
     
     
       4. The process of  claim 1  wherein the PLNG before being heated in step (a) has a temperature above about −112° C. (−170° F.) and a pressure sufficient for the liquid product to be at or below its bubble point. 
     
     
       5. The process of  claim 1  wherein the lean PLNG of step (e) has a temperature above about −112° C. (−170° F.) and a pressure sufficient for the liquid product to be at or below its bubble point. 
     
     
       6. A process for conveying natural gas containing C 3+  hydrocarbons, comprising the steps of: 
       (a) liquefying a natural gas stream to produce pressurized liquid natural gas (PLNG) containing C 3+  hydrocarbons and having a temperature above −112° C. (−170° F.) and a pressure sufficient for the PLNG to be at or below its bubble point;  
       (b) transporting the PLNG in one or more suitably pressurized containers onboard a floating vessel;  
       (c) removing the PLNG from at least one of the containers and heating the PLNG in at least one heat exchanger, thereby vaporizing at least a portion of the PLNG;  
       (d) passing the partially vaporized PLNG to a fractionation system;  
       (e) withdrawing a liquid stream enriched with C 3+  from a lower portion of the fractionation system;  
       (f) withdrawing a vapor from an upper portion of the fractionation system;  
       (g) cooling the vapor and thereby condensing the vapor to produce PLNG lean in C 3+ ;  
       (h) further conveying the PLNG of step (g); and  
       (i) heating the PLNG of step (h) to convert the PLNG to natural gas lean in C 3+ .  
     
     
       7. A process for removal of C 2+  or C 3+  hydrocarbons from a pressurized liquid natural gas (PLNG), comprising the steps of: 
       (a) heating the PLNG in a heat exchanger, thereby vaporizing at least a portion of the PLNG;  
       (b) passing the partially vaporized PLNG to a fractionation column;  
       (c) withdrawing a liquid stream enriched with C 2+  or C 3+  from a lower portion of the fractionation column;  
       (d) withdrawing a vapor stream from an upper portion of the fractionation column; and  
       (e) passing the vapor stream to the heat exchanger to condense the vapor to produce PLNG lean in C 2+  or C 3+ .  
     
     
       8. The process of  claim 1  wherein the removal of hydrocarbons less volatile than methane from a pressurized liquid natural gas (PLNG) is performed without external refrigeration. 
     
     
       9. The process of  claim 1  wherein the removal of hydrocarbons less volatile than methane from a pressurized liquid natural gas (PLNG) is performed without expansion cooling.